1. Field of the Invention
The present invention relates to an alloy suitable for severe oil and gas environments and, more particularly, to an ultra high strength alloy whose unique microstructure is obtained by special annealing and age hardening conditions, resulting in a combination of yield strength, impact strength, ductility, corrosion resistance, thermal stability and formability, making the alloy suitable for corrosive oil well applications that contain gaseous mixtures of carbon dioxide and hydrogen sulfide.
2. Description of Related Art
As shallow and less corrosive oil wells deplete, higher strength and more corrosion resistant materials are needed to allow for deeper drilling and for highly corrosive wells to operate successfully. Mildly corrosive wells are handled by various 13Cr steels. The 13% Cr alloys, however, lack the moderate corrosion resistance and strength required of deeper corrosive well applications that contain gaseous mixtures of carbon dioxide and hydrogen sulfide. Cayard et al., in “Serviceability of 13Cr Tubulars in Oil and Gas Production Environments,” published sulfide stress corrosion data that indicate 13Cr alloys have insufficient corrosion resistance for wells that operate in the transition region between sour gas and non-sour gas environments. NACE Paper No. 112, 1998, pp. 1-8, the contents of which are incorporated by reference herein.
Of further background are the following publications which are also incorporated by reference herein:
U.S. Pat. No. 4,788,036 dated Nov. 29, 1988, to Eiselstein et al.;
U.S. Pat. No. 6,458,318 dated Oct. 1, 2002, to Nishiyama et al.; and
Hibner et al. publication entitled “Comparison of Corrosion Resistance of Nickel-base Alloys for OCTG's and Mechanical Tubing in Severe Sour Service Conditions”, NACE Paper No. 04110, 2004, pp. 1-15.
Ni-base alloys are needed for the more highly corrosive environments. Commonly used high performance alloys for oil patch application, such as 925, 718, G-3, MP35N, TI-6246, C-276 and 725 are either too expensive or do not have the necessary combination of high strength and corrosion resistance. It is an object of this invention to provide a high strength and corrosion resistant alloy at a reasonable cost.